Repellent effect of topical deltamethrin on blood feeding by Culicoides on horses.

The research article investigates the effectiveness of using topical deltamethrin to deter blood feeding by Culicoides (biting midges) on horses. The research results indicate that there was no significant effect of treatment on the blood-feeding habits of these insects, suggesting that this method may not be effective in controlling the spread of African horse sickness.

Introduction and Methodology

• The researchers were spurred by the need for more effective ways of managing African Horse sickness, a disease spread by Culicoides biting midges. Notably, the UK’s Department for Environment, Food and Rural Affairs recommended topical deltamethrin for AHS control, but there was no scientific data to back its efficacy.
• To fill this knowledge gap, the researchers led a study investigating the effect of topical deltamethrin on blood feeding by Culicoides on horses, including which species of Culicoides feed on horses.
• They used three pairs of horses placed in partially enclosed cages. The cages were intended to allow samples representing the Culicoides interacting with each horse to be sampled.
• Four data collection sessions were done before a horse from each pair was treated with 10 ml of 1 per cent deltamethrin solution. This treatment process was followed by another four sessions of data collection.

Results and Findings

• Upon examination of the collected Culicoides, they found that the most common species were C. chiopterus, C. dewulfi, C. obsoletus, C. scoticus, C. pulicaris and C. punctatus. The prevalence of these species, combined with their higher likelihood for blood feeding, led researchers to posit these might be potential vectors for the AHS virus if it ever reached the UK.
• The other key finding in the study was that the use of deltamethrin had no significant effect on the blood feeding by the Culicoides. This refuted the assumption that its topical application would control the activity of these vectors on horses.

Conclusion

• The research concludes that the topical application of deltamethrin might not be reliable in preventing blood feeding by Culicoides on horses, contrary to previous beliefs and recommendations.
• An important caveat, however, is that the study did not explore the potential effect the widespread use of deltamethrin might have on the overall vector numbers or disease transmission from infected horses during an outbreak of African horse sickness.
• Thus, while the study questions the use of topical deltamethrin in individual horses, it acknowledges there might be a broader impact that was not studied. This leaves room for further investigation on the topic.